1. Field of the Invention
The present invention relates to percutaneous transluminal coronary angioplasty, and more particularly to a method for alleviating the myocardial ischemia generally associated with angioplasty.
2. Description of the Prior Art
Arteriosclerosis is a general term which refers to any pf a group of diseases in which the lumen of an artery becomes narrowed or blocked. The most common and important form of arteriosclerosis is the disease known as atherosclerosis. In atherosclerosis, material accumulates in the inner layer of an artery, narrowing of the arterial lumen. This, in turn, restricts the flow of blood through the artery. In fact, the flow of blood can become so restricted that it hinders the functioning of, or permanently damages, the organ which the artery feeds. These accumulations of material will hereinafter be referred to synonymously as lesions, plaques, or atheromas.
Atherosclerosis is treated by alleviating the diminished blood flow. This can often be accomplished by pharmacological therapy. For example, certain pharmacologicals can dilate the lumen of an affected artery, thereby restoring adequate blood flow. However, in most cases surgery is required to reestablish a lumen of proper diameter. A number of surgical procedures have been developed to this end. However, these procedures, such as arterial by-pass grafts, are major surgical operations, and accordingly, present a number of disadvantages to a patient, i.e., financial costs, inconvenience, discomfort, permanent disfigurement, and the risk of complications associated with any major surgery. In light of these disadvantages, methods of re-establishing proper lumen diameter in an occluded artery have been recently developed which are relatively non-invasive and present less risk to a patient than conventional surgery.
One such method is percutaneous transluminal coronary angioplasty, hereinafter referred to as angioplasty. Generally, angioplasty is preformed using a multi-lumen inflatable balloon catheter. At least one lumen of the catheter is open-ended allowing the passage of a guide-wire, or in some instances, the direct intra-arterial infusion of pharmacological agents. According to the procedure, the guide-wire is directed to the area of arterial narrowing using x-ray monitoring. Thereafter, the catheter is positioned, with the aid of the guide-wire, in the region of arterial narrowing. Concentric with the lumen including the guide-wire is a second lumen which connects to an elongated inflatable segment, or balloon portion, near the distal end of the catheter. The second lumen and balloon are generally filled with diluted contrast medium. The contrast medium is a radio-opaque liquid which makes visualization of the catheter possible by means of fluoroscopy.
Typically, the procedure for angioplasty involves first selecting a convenient place to introduce the catheter into the arterial system of the patient, for example, the femoral artery of the leg. Next, the catheter is guided to the affected artery, for example, the left anterior descending coronary artery. This is done manually with the aid of fluoroscopy. When the catheter is appropriately positioned, the guide-wire is advanced to and passed through the point of obstruction. The balloon catheter, which surrounds the guide-wire, is then advanced along the guide wire until it is surrounded by the occluding atheroma. The balloon, which is constructed of material having a high tensile strength and low elasticity, is then inflated. As the balloon expands it deforms the occluding atheroma adjacent to its surface. This creates a larger inner diameter within the occluded artery. The usual method is to repeat the inflation an arbitrary number of times. It is hoped that by repeatedly deforming the occluding atheromas they will become permanently deformed, thus providing the affected artery with a lumen having a sufficient inner diameter. Further, it is believed that by prolonging the rate that the balloon is inflated reduces the possibility of re-stenosis. By reducing the rate at which the balloon is inflated, the atheroma is slowly stretched and deformed, it is believed that the combination of these actions reduces the likelihood of re-stenosis. The balloon is then collapsed and retracted. The site of the obstruction is then examined angiographically. This is often accomplished by injecting a radio-opaque dye through lumen housing the guide-wire. If the artery is still occluded, the procedure is repeated.
Standard angioplasty protocol requires that the balloon is inflated for a period of about 60 seconds. During this period, the flow of blood through the artery is blocked, and the supply of blood perfusing tissue past the blockage becomes inadequate to sustain cellular metabolism, a condition known as ischemia. If the ischemic episode is prolonged, the affected tissue will die, a condition known as infarction. For example, when angioplasty is performed to reduce an $ occlusion in a coronary artery, e.g., percutaneous transluminal coronary angioplasty, myocardial tissue downstream from the inflated balloon becomes ischemic. The extent of damage to the myocardial tissue and the morbidity of the corresponding pathological syndrome depends greatly on the length of time the blood flow is interrupted. Symptomatic o myocardial ischemia caused by angioplasty are characteristic severe chest pain and electrocardiogram (ECG) changes, e.g., ST segment elevation. Further, if the ischemic episode is not promptly resolved, infarction, dysrhythmia, and possibly death will occur.
Because of the accompanying pain and possibility of infarction and dysrhythmia, present angioplasty procedures only allow the balloon to remain inflated for about 60-120 seconds. Since the balloon remains inflated for such a short period of time, the procedure is very inefficient, and the inflation of the balloon must be repeated several times. Further, repeated inflations increase the likelihood of re-stenosis. In order to increase the efficiency of the procedure and decrease the likelihood of re-stenosis, it would be advantageous to prolong the balloon inflation time. A method to prolong balloon inflation time while at the same time decreasing patient pain and risk of complications would be a substantial improvement over present state-of-the-art percutaneous transluminal coronary angioplasty procedures.